(04) agenda interface layer media switching...

By:Dr. Ahmed ElShafee

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I١

Lecture (04)Network interface

Layer media & switching I

Agenda• Physical layer : transmission media• GUIDED MEDIA• UNGUIDED MEDIA: WIRELESS• Switched communication network• Circuit switching technology• Packet switching technique

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I٢

Physical layer : transmission media•

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I٣

Data link

Internetwork

Transport

Applications

Data link

Internetwork

Transport

Applications

Netw

ork

Interfa

ce

Netw

ork

Interfa

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• Classes of transmission media

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I٤

GUIDED MEDIA• Guided media, which are those that provide a conduit from

one device to another, include – twisted‐pair cable, – coaxial cable, and – fiber‐optic cable.

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I٥

• Twisted‐pair cable

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• UTP and STP cables

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• UTP connector

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• UTP performance

• gauge is a measure of the thickness of the wireDr. Ahmed ElShafee, ACU : Fall 2015, Networks I١٠

• Coaxial cable

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I١١

• Categories of coaxial cables

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• BNC connectors

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• Coaxial cable performance

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I١٤

• Optical fiber

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• Fiber construction

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• Fiber-optic cable connectors

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• Bending of light ray

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• Propagation modes

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•

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I٢٠

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I٢١

UNGUIDED MEDIA: WIRELESS• Unguided media transport electromagnetic waves without

using a physical conductor. • This type of communication is often referred to as wireless

communication.

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I٢٢

• Electromagnetic spectrum for wireless communication

• Radio waves are used for multicast communications, such as radio and television, and paging systems.

• Microwaves are used for unicast communication such as cellular telephones, satellite networks,and wireless LANs.

• Infrared signals can be used for short‐range communication in a closed area using line‐of‐sight propagation.

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I٢٣

• Propagation methods

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I٢٤

• bands

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• Wireless transmission waves

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• Omnidirectional antenna

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• Unidirectional antennas

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switched communication network

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Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I

switched communication network (cont,..)Terminologies:• For transmission of data beyond a local area, communication

is achieved by transmitting data from source to destination through a network of intermediate switching nodes;

• The switching nodes are not concerned with the content of the data their purpose is to provide a switching facility that will move the data from node to node until they reach their destination.

• Stations: The devices attached to the network, computers, terminals, telephones, or other communicating devices

• Node: switching devices whose purpose is to provide communication

• transmission links: connection between nodes and terminals٣٠

switched communication network (cont,..)• Node‐node links are usually multiplexed, using either

frequency division multiplexing (FDM) or time division multiplexing (TDM).

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switched communication network (cont,..)

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switched communication network (cont,..)

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How it works?• data entering the network from a station are routed to the

destination by being switched from node to node.• data from station A intended for station F are sent to node 4. • They may then be routed via nodes 5 and 6 or nodes 7 and 6

to the destination.

switched communication network (cont,..)Topology:• Each station attaches to a node• Some nodes connect only to other nodes (eg., 5 and 7). • Other nodes have one or more stations attached as well (such

nodes accept data from and deliver data to the attached stations.)

• It’s recommended that each connection has more than one possible path through the network for each pair of stations. • This enhances the reliability of the network. ٣٤


switched communication network (cont,..)Switching technologies• Two different technologies are used in wide area switched

networks: circuit switching and packet switching. • These two technologies differ in the way the nodes switch

information from one link to another on the way from source to destination.

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Circuit switching technology• there is a dedicated communication path between two

stations. • That path is a connected sequence of links between network

nodes. • On each physical link, a logical channel is dedicated to the

connection. • Communication via circuit switching involves three phases:

– Circuit establishment– Data transfer– Circuit disconnect

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Circuit switching technology (cont,..)Circuit establishment –• Before any signals can be transmitted, an end‐to‐end (station‐

to‐station) circuit must be established.Data transfer –• Data can now be transmitted through the network between

these two stations. • The transmission may be analog or digital, depending on the

nature of the network. • Generally, the connection is full duplex.

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Circuit switching technology (cont,..)Circuit disconnect –• After some period of data transfer, the connection is

terminated, usually by the action of one of the two stations. • Signals must be propagated to the intermediate nodes to

deallocate the dedicated resources.

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Circuit switching technology (cont,..)Disadvantages• Circuit switching inefficient.• Channel capacity is dedicated for the duration of a

connection, even if no data are being transferred• For a voice connection, utilization may be rather high, but it

still does not approach 100%. • For a client/server or terminal‐to‐computer connection, the

capacity may be idle during most of the time of the connection.

• there is a delay prior to signal transfer for call establishment.

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Circuit switching technology (cont,..)AdvantagesHowever, once the circuit is established, the network is

effectively transparent to the users.

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Circuit switching technology (cont,..)Public Switched Telephone network

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Circuit switching technology (cont,..)• Circuit switching was developed to handle voice traffic but is

now also used for data traffic.• The best‐known example of a circuit‐switching network is the

public telephone network• collection of national networks interconnected to form the

international service.• A public telecommunications network can be described using

four generic architectural components:

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Circuit switching technology (cont,..)• Subscribers: The devices that attach to the network, typically

telephones, percentage of data traffic increases year by year.• Subscriber line: The link between the subscriber and the

network, also referred to as the subscriber loop or local loop, mostly using twisted‐pair wire.

• Exchanges: The switching centers in the network. A switching center that directly supports subscribers is known as an end office.

• Trunks: The branches between exchanges. Trunks carry multiple voice frequency circuits using either FDM or synchronous TDM

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Circuit switching technology (cont,..)Circuit Establishment

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Circuit switching technology (cont,..)• Subscribers connect directly to an end office, which switches

traffic between subscribers and between a subscriber and other exchanges.

• The other exchanges (intermediates) are responsible for routing and switching traffic between end offices.

• To connect two subscribers attached to the same end office, a circuit is set up directly between them.

• If two subscribers connect to different end offices, a circuit between them consists of a chain of circuits through one or more intermediate offices.

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Circuit switching technology (cont,..)

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• “a” connection is established between lines “a” and “b” by simply setting up the connection through the end office.

• The connection between “c“ and “d” is more complex. • In “c”’s end office, a connection is established between line

“c” and one channel on a TDM trunk to the intermediate switch.

• In the intermediate switch, thatchannel is connected to a channelon a TDM trunk to “d”'s end office. In that end office, the channel is connected to line d.

Circuit switching technology (cont,..)key requirements for voice traffic• virtually no transmission delay • certainly no variation in delay.• A constant signal transmission rate • The quality of the received signal is sufficiently high.

These requirements are necessary to allow normal human conversation.

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Circuit switching technology (cont,..)Conclusion• Circuit switching , well suited to the analog or digital

transmission of voice signals• In today‘s digital world, Circuit switching is inefficient ,

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Circuit Switch Elements (digital switch)

• A network built around a single circuit‐switching node consists of a collection of stations attached to a central switching unit.

• The central switch establishes a dedicated path between any two devices that wish to communicate.

Circuit switching technology (cont,..)

Circuit switching technology (cont,..)• The heart of a modern system is a

digital switch. digital switch• Its function is to provide a transparent

signal path between any pair of attached devices.

• The path is transparent to the attached pair of devices that there is a direct connection between them.

• connection must allow full‐duplex transmission.

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Circuit switching technology (cont,..)Components• network interface• Control unit1. network interface • element represents the functions

and hardware needed to connect digital devices, such as data processing devices and digital telephones, to the network.

• Analog telephones can also be attached if the network interface contains the logic for converting to digital signals. ٥١


Circuit switching technology (cont,..)• Trunks to other digital switches carry

TDM signals and provide the links for constructing multiple‐node networks.

2. control unit performs three general tasks: 1. Establishes connections; as

requested by the attached device. 2. Maintains the connection; because

the digital switch uses time division principles, this may require ongoing manipulation of the switching elements.

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• Tear down the connection; either in response to a request from one of the parties or for its own reasons.

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Thanks,..See you next week (ISA),…

Dr. Ahmed ElShafee, ACU : Fall 2015, Networks I٥٤

(04) agenda interface layer media switching...

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